(1) Field of the Invention
The present invention relates to a collective housing intercom system for a collective housing such as an apartment house and, more particularly, to a collective housing intercom system having a technique for compensating the level of a video signal taken by the camera of a main entrance station.
(2) Description of Related Art
In the prior art, the collective housing intercom system of this kind is exemplified by that (as referred to Non-Patent Document 1) which can display the image (or the video signal) taken by the camera of a main entrance station in the monitor of a predetermined residential master station (or a calling partner).
Non-Patent Document 1: General Catalogue 2005/2006 Edition (pages 145, and 148 to 151), issued by Aiphone Co., Ltd.
According to the collective housing intercom system of Non-Patent Document 1 described above, however, the video signal taken by the camera of the main entrance station is transmitted in a base band to a specific residential master station so that the level attenuates according to the distance of the line length of the line through which the video signal is transmitted. As a result, the image taken by the camera of the main entrance station may be displayed as a deteriorated image of poor visibility in the monitor of the residential master station.
The present invention has been conceived to solve the problem described hereinbefore, and has an object to provide a collective housing intercom system capable of displaying a satisfactory image having not deterioration but excellent visibility in the monitor of a residential master station, irrespective of the long distance of a line through which the video signal is taken by the camera of the main entrance station.